Anti-HIV topical microbicides are an accessible means to minimize HIV transmission. Certain HIV reverse transcriptase inhibitors (RTIs) are promising microbicide candidates and microbicides based on NNRTI's (UC781 and TMC120) as well as one with a nucleotide RT inhibitor (PMPA; tenofovir) are in Phase 1 clinical trials. However, there is a definite need to identify new pipeline RTI's as backup microbicidal agents as it is well known that many drugs with promising preclinical properties fail during advanced clinical evaluation. The novel NNRTI 5-chloro-3-(phenylsulfonyl)indole-2-carboxamide (CSIC) may represent an important pipeline drug as our preliminary data suggest that the in vitro microbicidal efficacy of CSIC is as good or superior to that of UC781. Combination microbicides directed at different HIV targets may be preferable and we propose that the combination of CSIC and the HIV entry inhibitor antimicrobial peptide RC-101 will provide superior broad spectrum anti-HIV microbicidal activity. In this context, we propose the following Specific Aims for this Program Project component: (1) To evaluate the in vitro microbicidal properties of CSIC alone and in combination with RC-101; (2) To determine the mechanism of the CSIC-induced protective or memory effect; (3) To determine whether microbicides based on CSIC alone and in combination with RC-101 will select in vitro for transmission of NNRTI-resistant virus; and (4)To develop and validate an analytical method to quantify the plasma, cellular and tissue levels of CSIC following vaginal or rectal topical administration in monkeys (Project 4).